Beric Dondarrion

The young, handsome Lord of Blackhaven, one of the castles of the Dornish Marches. Red of hair, he is betrothed to Lady Alia Dayne and has her nephew as his squire.

It’s unclear that Edric Dayne will appear on the show. Besides this, Dormer seems to match the character reasonably well, other than being rather older. It should be noted that the role was played by a featured extra in the first season, but was recast for the third season.